Electrodeposition of CuIn1-xGaxSe2 Solar Cells on a Transparent Conducting Back Contact

In this study, a CuIn_1-xGa_xSe₂ (CIGS) absorber layer was grown on a transparent conducting oxide (TCO) back contact to form a semi-transparent solar cell by electrodeposition. Experimentally, the crystalline quality and the film stoichiometry of the electrodeposited CIGS films can be improved by a post-heating treatment combined with selenization. The resulting CIGS films exhibit the (112)-preferred orientation of the chalcopyrite structure. In addition, the selenization process provided atomic ratios equivalent to 1.02, 0.84 and 0.09 respectively for Cu/(In+Ga), Se/(Cu+In+Ga) and Ga/(In+Ga). As evaluated from the cathodoluminescence (CL) spectrum of the CIGS films, the lower bandgap value of 0.97 eV could be attributed to the difficulty of incorporating Ga atoms associated with the discrepancy of the reduction potentials in the aqueous solution containing 12 mM CuSO₄, 25 mM In₂(SO₄)₃, 28 mM Ga₂(SO₄)₃, and 25 mM SeO₂. Finally, these CIGS solar cells exhibited improved photovoltaic properties in the short-circuit current density (4.04 mA/cm²) and the open-circuit voltage (0.15 V). The improvement may be due to the improved interfacial quality between the CdS and CIGS layers as the CIGS films are electrodeposited in the modified electrolyte with half of their original concentration.